ABSTRACT The overall goal of this project is to develop a highly effective and safe nanomedicine for systemic lupus erythematosus (SLE) or lupus. Among many medications used in clinical management of lupus, glucocorticoid (GC) is most widely used because of their high anti-inflammatory potency. But their notorious toxicities have hampered the long-term clinical application. To reduce their side effects, we have conjugated dexamethasone (Dex, a potent GC) to N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer and found that the Dex prodrug is nephrotropic in a mouse model of lupus nephritis (NZB/W F1). Prophylactic and treatment of established lupus nephritis with a monthly P-Dex injection (i.v.) are much more effective in prevention and reduction of albuminuria than dose equivalent daily free Dex treatment. The P-Dex treatment did not elicit osteoporosis, but other GC side effects (e.g. adrenal gland atrophy) remained. To further address this challenge, we recently designed a novel prodrug nanomedicine by conjugating Dex to polyethylene glycol (PEG). The resulting amphiphilic PEG-Dex self-assembles into micelles. When tested in the NZB/W F1 mice, it demonstrated potent therapeutic efficacy, similar to P-Dex, but did not show any classical GC side effects. Based on these exciting preliminary data, we hypothesize that due to their different structural design, P-Dex and PEG-Dex have very different pharmacokinetic/biodistribution (PK/BD) profiles and patterns of interaction with the cellular components of the immune system, leading to distinct subcellular distribution/activation patterns, similar therapeutic potency, but different safety profiles. We also speculate that the original structural design of our lead candidate, PEG-Dex micelle may not always work as well in other lupus models due to the heterogeneity and comorbidities of lupus disease, which would necessitate further structure optimization. To validate these hypotheses, we propose first to perform a head-to-head comparative PK/BD study of PEG-Dex and P-Dex. We will also analyze the PK/BD profiles of the free Dex released from the two prodrug nanomedicine. These studies may partially explain why PEG-Dex micelle has lower toxicity than P-Dex and will illustrate its working mechanism from the PK/BD aspect. Second, we will perform in vitro and in vivo cellular studies to compare and analyze the interaction of P-Dex and PEG-Dex with various cellular components of the immune system and their impact on the biological functions of the prodrug nanomedicine. The results from this study will further explain why PEG-Dex shows much better safety profile than P-Dex on the cellular and molecular levels. Third, we will validate PEG-Dex micelle's efficacy and safety in NZM2410, MRL/lpr and CIA mice because of the heterogeneity and comorbidities of lupus disease recapitulated in these models. Based on the experimental feedback, the structure of PEG-Dex micelle will be optimized and the resulting final drug candidate will be evaluated in NZB/W F1 mice for 1 year to confirm its long-term efficacy and safety in preparation for its clinical translation.